I finally saw Ratatouille the other night (having older children means not seeing it in the theaters, and having doting in-laws means the kids will first see it on a night when I am out).
I liked the movie, but not nearly as much as Finding Nemo or The Incredibles. I thought the plot was a little hard to relate to, and I didn't like the ending. It seemed mean (after a great conversion to light, Anton Ego's career is demolished and mentioned almost as an afterthought) and inexplicable (Gusteau's closes because of rats, then they open a new restaurant full of rats anyway).
As always, the look of the movie is remarkable. Most Pixar movies have a signature challenge: Monster's Inc had fur, Finding Nemo had water, The Incredibles had clothing and hair. Ratatouille has food. In each case, the goal is to model a familiar component of the real world well enough that it can add to the story telling rather than detract from it. Meeting those challenges is a huge technical achievement, and going behind the scenes to see the effort is eye-opening.
Pixar maintains an online library of technical papers explaining some of their technology. Some are single pages, others are 100-page course notes. Browsing through them, you get a sense of the obsessive details that have to be dealt with. As an unexpected example, the kitchen scenes in Ratatouille are filled with cooks chopping food. One approach would be to assign some junior animators to animate the process of slices peeling off a zucchini. Another is to procedurally model a cutting object which can deform and remodel another object. Pixar chose this last approach both for its greater fidelity, and also to free the animator to focus on the storytelling.
The papers in the library offer glimpses of the amount of work required to make a movie like this. Traditional animation required legions of artists to draw everything. CGI animation also requires enormous effort, but finely sliced into different disciplines: animators to imbue objects with life, modelers to create those objects in ways that simplify the animators' jobs, and technical staff to create the universe in which the movie takes place.